It is well known to control trachea and varroa mites in a beehive by release of formic acid by evaporation at a controlled rate so as to achieve a concentration of acid fumes just below that of being harmful to the bees. In the prior art applicant is aware of German Patent No. 3427330 to Kramer. Kramer discloses a device for combating varroa mites in beehives where the device consists of soft fibre plates impregnated with formic acid and enclosed in a perforated plastic bag. In particular, the Kramer device consists of a 250-650 square centimeter soft fibre plate having 10 millimeters thickness which may be impregnated with 200-300 millilitres of concentrated formic acid. The soft fibre plate may be enclosed in a plastic film bag having 5-15 perforations on each side of the plate for a total exit area of 15-55 square centimeters.
Kramer teaches that, when placed horizontally in the hive over the brood area and above the brood chambers of the bee population, that the soft fibre plate formic acid dispenser controls varroa mites without harming the bees. The size of the fibre of plate and extent of the perforation of the plastic bag result in controlled release of 85% formic acid concentration over a period of 7 days in August and 14 days in October.
There are many different ways of dispensing acid. They require multiple applications, or several adjustments to openings or cutting slots. They work on the principle of absorbency and evaporation by regulating the wrap openings. Generally, these dispensers are placed on the top of the cluster or on the bottom board. They may or may not work equally on colonies of different sizes. They also require additional space and equipment.
As reported in the American Bee Journal (March, 1996, at pages 190-192), the Kramer soft fibre plates are made of Pavatex™ and the plastic bags are of 0.15 millimeter thickness. For storage the plates are kept frozen and the plastic container kept air tight. Before application, the necessary evaporation holes are made in the plastic casing with a round punching tool of 1.5 centimeters diameter. The number of holes varies according to the hive system and climate including the microclimate of the apiary. For a treatment, the plates are hung into the empty honey chamber by means of a honeycomb frame for seven days. For medium sized one story hives, Kramer teaches that a distance of 5 centimeters should be kept between the brood combs and the board.
The treatment efficiency of this method depends on the formic acid concentration in the hive air and on the duration of the treatment. It can be controlled on the basis of the amount of evaporated formic acid. Thus, the board has to be weighed before and after the treatment. If there is an evaporation of more than 7 grams of formic acid (85% concentration) per day, a treatment efficiency of more than 95% may be expected. If less than 7 grams evaporate, the treatment efficiency will be insufficient. To be reused, the Kramer plates must be reimpregnated with formic acid up to their gross weight of 250 grams of formic acid.
Acid is sold at an 85% concentration. At this concentration, acid evaporates faster introducing acid at a damaging rate exceeding the bees' ability to ventilate and causing losses of young and old queens as well as brood. At 73%, formic acid and water evaporate equally at the evaporating surface. At 65% water evaporates faster. Evaporation of water at the evaporating surface creates a gentle introduction of acid into the hive and eliminates young queen losses and brood mortality.